Rotary lobe pumps fall into the category of displacement pumps and have two rotary lobes each with two or more rotary lobe vanes. The rotary lobes are disposed in a housing, the inner wall of which faces the rotary lobes and the outer wall of which encloses the rotary lobe pump on the outside. With its inner wall, the housing encloses respective sections of the outer peripheries of the rotary lobes. The section enclosed by the inner housing wall is also referred to as the enclosed angle. The tips of the rotary lobe vanes may be provided with a coating, preferably a sealing face made of rubber, in order to create a seal between the rotary lobe vanes and the inner housing wall and between the rotary lobe vanes as they engage with each other. The rotary lobes are each driven rotatably about a rotational axis in respective opposite directions, an outer periphery of each rotary lobe being defined by the circular paths on which the tips of the rotary lobe vanes turn. In the region in which the rotary lobe vanes engage with each other, the two outer peripheries of the rotary lobes intersect. Rotary lobe pumps are generally symmetrical in structure in order to allow the feeding direction to be reversed.
Rotary lobe pumps with the type of construction initially specified are known, for example, from DE 297 23 984 U1, DE 34 27 282 A1, U.S. Pat. No. 2,848,952, NL 101 62 83, U.S. Pat. No. 3,126,834 and U.S. Pat. No. 15,221. Rotary lobe pumps of this kind are also used to convey media which contain solids. A fluid medium, generally a liquid which may contain various kinds and amounts of solids, is fed through the inlet opening into the region where the rotary lobes intersect and is displaced onwards to the outlet opening by the rotary lobe vanes. Media of different viscosities may be conveyed. Rotary lobe pumps of the kind initially specified have feed rates ranging, for example, from approximately 3 to 1,000 cubic meters per hour, i.e., approximately 50 to 16,667 liters per minute, and pressures of up to approximately 16 bar.
Solids contained in the medium are swept with the medium into the cavities between the rotary lobe vanes and transported with the medium in the feeding direction of the rotary lobe pump from the inlet opening to the outlet opening. Solids contained in the medium may be stones, metal parts or other foreign matter, for example.
Rotary lobe pumps are frequently deployed in challenging environments. Typical fields of application for rotary lobe pumps are, for example, sewage plants, black water and wastewater engineering, disposal and recycling engineering, the paper and cellulose industry, rail and opening operations, the food industry and the construction industry. Rotary lobe pump are used, inter alia, as sludge pumps, wastewater pumps, black water or grey water pumps, thick matter pumps, animal feed pumps, mobile pumps, pumps for media contaminated with foreign matter, liquid manure pumps, feces pumps or pumps for stillage and pulp. These deployment contexts require rotary lobe pumps to have a robust, reliable and tough design.
However, pump component damage, shut-downs and severe wear and tear are recurrent phenomena in the case of existing rotary lobe pumps, as solids are not always transported in their entirety into the cavities between the rotary lobe vanes, where they are displaced onwards, but may become trapped between the rotary lobe vanes and the housing, or between two rotary lobe vanes as they engage with each other. Solids may become stuck between rotary lobe vanes and the housing, or between two rotary lobe vanes of the two rotary lobes as they engage with each other, which may result in the pump shutting down, in damage or wear of the housing and/or of the rotary lobes, in particular of the rotary lobe vanes and in particular of any (sealing) coating on the tips of the rotary lobe vanes. Shut-downs lead to unwanted operational disruptions and damage, and wear and tear of the rotary lobes and/or the housing result in reduced efficiency of the pump due to reduced feed pressure and in higher costs due to the need for repairs and for the replacement of wearing parts and replacement parts.
In order to eliminate these disadvantages, it is proposed in DE 20 2005 010 467 U1 and in DE 20 2006 020 113 U1 held by the applicant that the housing enclose the outer peripheries of the rotary lobes beyond a housing half angle α of 90° on the inlet side and on the outlet side, as shown in FIG. 1. Although the above disadvantages can be decreased as a result of this reduction in the cross-section of the inlet opening and outlet opening on the inner wall of the housing, there is still a need for further improvement of rotary lobe pumps in order to prevent the disadvantages mentioned above.